This application is being submitted by a group of eight investigators who use immunofluorescence microscopy as a significant part of their research effort. All are using this technique to localize molecules that are spatially distributed through individual cells or in small animals. Wide field immunofluorescence microscopy has the disadvantage that light from above and below the plane of focus blurs the image and so limits the information that can be obtained by this technique. This technical problem has been overcome by the development of laser scanning confocal microscopy. We are requesting funds to purchase a Bio-Rad MRC-600 Confocal Fluorescence Imaging System and a dedicated Zeiss microscope. The eight laboratories (funded by 12 NIH grants) cover a large range of research topics, all of which would greatly benefit by the application of confocal microscopy. These topics include studies on the structure and assembly of the cytoskeleton (Drs. Bretscher and Quaroni), on the spatial and temporal organization of internal membranes (Dr. Brown), on the detailed structure of the mitotic spindle in wild-type and mutant Drosophila (Dr. Goldberg), on the cytoskeletal organization during early development in wild-type and mutant embryos of Caenorhabditis (Dr. Kemphues), on the distribution of proteins that regulate the cell cycle, cell-to-cell communication and cellular transformation (Dr. Shalloway), on the structure of the neuromuscular junction (Dr. Salpeter), and pronuclear fusion and secretory products of the male accessory gland in Drosophila (Dr. Wolfner). The proposed confocal microscope will be housed in the Flow Cytometry/Video Microscopy Facility of the Cornell University Biotechnology Program which will make available a full-time technician to run the instrument. Further technical support, should it be necessary, will be provided by the NIH BIomedical Research Technology Resource and NSF National Instrumentation Facility for Optical Microscopy at Cornell University, directed by Dr. Watt W. Webb.